Common computer-jargon term to refer to arbitrary-precision math and data-types. The term "arbitrary-precision" refers to the ability of a machine to perform numerical computations whose precision is limited only by the available memory.

My first thought is that they're the same. However while writing this meta question I found some information that made me thinks one is about integer and the other includes rational values. But then from the bigint wiki

Several modern programming languages have built-in support for bignums, and others have libraries available for arbitrary-precision integer and floating-point math. Rather than store values as a fixed number of binary bits related to the size of the processor register, these implementations typically use variable-length arrays of digits.

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Big ints can also be used to compute fundamental mathematical constants such as π to millions or more generally to investigate the precise behaviour of functions such as the Riemann zeta function where certain questions are difficult to explore via analytical methods. Another example is in rendering fractal images with an extremely high magnification.

i always though bignum was for handling decimal and bigint wasfor whole numbers?
– user623150Jan 12 '18 at 11:13

3

Unsurprisingly, bigint is also used for the actual BIGINT type found in many SQL dialects, which is usually just a 64-bit integer (that is, one step above INT). A topic which arguably does not deserve its own tag, but is not related to arbitrary precision (and I'm not aware of any database system with native support for that).
– Jeroen MostertJan 13 '18 at 16:49

Isn't one of these (Bignum?) also the formal name of a library? And it appears that both bigint and bignum (with various different case) are variables in some languages.
– LundinJan 15 '18 at 10:16

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The different kinds of "number too large for hardware representation" have more in common than different. The differences that exist are going to be implementation-specific to a large extent, and a useful library that provides integers is most likely going to provide rationals or reals of some kind as well.
– LeushenkoJan 15 '18 at 10:25